The present invention relates to liquid crystal displays and, more particularly, to an improved arrangement for sealing apertures in the glass walls of such displays.
In the manufacture of liquid crystal displays the liquid crystal material is contained within a glass enclosure formed by sealing a pair of spaced glass plates at their periphery to leave an inner cavity there between. The liquid crystal material is inserted into this cavity through one or more fill ports in one of the glass plates. The insertion of the liquid crystal material is one of the final steps in the manufacture of a liquid crystal display to avoid overheating as well as possible decomposing of the liquid crystal during heat-sealing of the glass plates.
Once the liquid crystal material is in place, it is necessary to provide a relatively strong seal for the fill ports with the seal matched to the characteristics of the surrounding glass enclosure.
Although it is common to seal glass liquid crystal display enclosures with plastic (hydrocarbon) sealants, a glass seal is generally preferred for demanding service specifications and for long-life designs. A glass seal is more readily matched in thermal expansion characteristics with the glass enclosure and is relatively inert chemically, so that it is unlikely to react adversely with the liquid crystal contents. However, because of problems related to the overheating and/or chemical contamination of the liquid crystal, no glass seal design has proved practical and commercially feasible. The present invention is directed toward providing such a commercially acceptable glass seal and, surprisingly, with the use of relatively inexpensive, readily available, easily processed sealant components.
Several problems contribute to the present inability to develop an acceptable glass bead seal which could be heated within the fill port to melt and bridge the port. Some related obstacles are the possibility of overheating the liquid crystal within the cell and degrading its characteristics as well as developing bubbles and deleterious gas emissions and seal-pressures therefrom. Also certain evolving by-products may react adversely with the crystal.
Glass bead sealing techniques involve heat distribution problems. Ideally, the heat necessary to melt and fuse the bead should be confined to the bead alone and not be allowed to spread to the surrounding glass and/or the liquid crystal. This conserves heat as well as avoids damaging the cell. The present state of the art discloses no practical means of achieving this.